The proposed research is directed toward obtaining detailed information on the three-dimensional structure and nature of the active site(s) of the two cannabinoid receptors (CB1 and CB2). Such information is of fundamental importance in understanding the mechanism of action of cannabinoids at the molecular level and for designing potent and selective cannabinoid analogs for each of these two receptors. The aim of this proposal is to develop novel high affinity covalent probes for the two cannabinoid receptors. A number of such probes possessing reactive groups at strategic positions will be designed, synthesized and tested for their affinities for CB1 and CB2 receptors. Hopefully some of these probes will be able to discriminate between the two receptors. The conformation of all analogs in solution will be studied by high resolution multidimensional NMR spectroscopy and computational methods in order to compare their relative stereoelectronic properties. Some probes possess two irreversible groups and will be used to covalently label the cannabinoid receptors at two amino acid residues at or near the active site(s). Analysis of the amino acid residues involved in covalent attachment of the ligands should provide useful information on the structure of the active site(s). The information obtained from this work will be used to design therapeutically useful cannabinoids.